The layer-structure transition of glass-fiber-reinforced composite materials

This study aims to investigate whether the layer-structure transition governed by fiber orientation is caused by the change in the elongational strain field or by the change in the shear strain field during the filling process in injection molding using short-fiber-reinforced thermoplastic resin. To this end, a polyamide 6 containing 30 wt% of short-fiber glass was compounded, and a simple plate was injection-molded. The fiber orientation of the plate was observed via X-ray computed tomography, and the fiber orientation distribution was quantified as fiber orientation tensors. The transition of the layer structure, which is mainly composed of the shell layer and core layer during the filling process, was evaluated on the basis of the fiber orientation distribution. The experimental results were compared with velocity information obtained via flow analysis of elongational and shear strain fields. The results showed that flow induction affects the layer-structure transition and that the transition occurs because of changes in the elongational strain field and not because of changes in the shear strain field during the filling process. Thus, the elongational strain field is an important consideration when modeling fiber orientation.